Conventional air bags include an inflator and an air bag, or cushion, having a predetermined inflated volume. When actuated, the inflator inflates the airbag at a rate determined by the rate of gas generation by the inflator. This system treats all passengers and all crashes the same. However, it is known that vehicle occupants vary in size, weight, and seat position and seat belt usage. Also, crashes vary in severity of deceleration forces experienced by vehicle occupants. Thus, all of these variables produce varying conditions, which are experienced by air bag systems.
Air bag systems are currently being developed to include enhanced sensing of vehicle occupant size, weight, seat position and seat belt usage, and crash severity. Much development is occurring to tailor the performance of these systems to vehicle occupants' specific needs. Much of this development centers on varying the inflation rate of the airbags.
In situations where low inflation rate air bag deployment is desired, air bag volume may be too great for the system to maintain optimal occupant protection. If a cushion is underinflated, the occupant must penetrate the air bag some distance before internal air bag pressure becomes sufficient to restrain the occupant.
Currently, there are two types of driver air bags: face bags and full size bags. The former (roughly of 40 liter size) are used in areas where seatbelt usage is high, such as in Europe, while the latter (roughly 60 liter size) are primarily used in the United States where seat belt usage is lower and where government regulations require validation in unbelted occupant testing. Such a variable volume air bag, used in conjunction with a seatbelt buckle sensor, could offer an appropriate amount of restraint. In this manner, an unbelted occupant would experience a full torso and head restraint, while a belted occupant would experience head and face restraint.